The primary objective of this three-year grant is to design a fourth (and final) version of the dual-Purkinje-image eyetracker and to make this instrumentation available to the eyetracker-user community. During the first and second years, we achieved major improvements in system noise (less than 1 minute of arc) and frequency response (system delay of approximately 0.5 ms). Perhaps most important was the development of an automated three-axis alignment platform (on which the instrument is mounted) and the associated electronic control circuitry required. With this new feature, the eyetracker automatically aligns to the subject, and greatly increases the usefulness of the instrument. All of these design improvements and new features represent a major advance over the performance and ease of use of the third-generation eyetracker and reassures us that the fourth-generation instrument, to be completed during the final year of the grant, will represent a significant research and clinical instrument.